Pyrotechnic yellow smoke compositions based on solvent yellow 33

ABSTRACT

A yellow smoke composition useful in hand held signals, such as the U.S. Army M194 yellow smoke parachute signal; which composition contains the nontoxic, environmentally safe, quinoline solvent yellow 33 color agent and critically exhibits the requisite dense yellow smoke for the requisite 9 to 18 second burn time upon use. Further, this inventive yellow smoke composition can be used in current metal tubes and in other media, such as biodegradable cardboard tubes.

FEDERAL RESEARCH STATEMENT

The inventions described herein may be manufactured, used and licensedby, or for, the U.S. Government, for U.S. Government purposes.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to hand held signal pyrotechnic smokecompositions, and more particularly, to such an compositions that arefree of the conventional, but toxic yellow smoke agents Vat Yellow 4(dibenzochrysenedione) and benzanthrone, and still continue to providethe requisite density, burn time, and good color quality.

2. Background Art

Hand held signal (HHS) pyrotechnic smoke compositions are useful formultiple military purposes—including signaling troop locations ordistress, during combat or training operations, or to serve as a beaconfor target or landing zone marking. One such pyrotechnic smokeformulation is contained within the US Army M194 HHS—which HHS islaunched via a rocket to a height of about 725 feet, at which point thesignal is ignited. The M194 HHS provides a dense, highly visible yellowsmoke as it falls back to earth via parachute—burning for 9 to 18seconds (ideally about 13 to about 15 seconds), while producing thedesired yellow smoke during this period, before burnout at about 500 to600 feet. Unfortunately, the current M194 HHS yellow smoke formulationcontains two toxic anthraquinone dyes, namely Vat Yellow 4 (aka(dibenzochrysenedione) and benzanthrone. Benzanthrone is a known dermalsensitizer, and is reported as causing liver and nervous system damage;plus, it is also known to be highly toxic to aquatic life. Vat Yellow 4,felt to contain small but significant amounts of dibenzochrysene (anextremely potent carcinogen) is classified as a Group 3 material by theInternational Agency for Research on Cancer (IARC)—because of evidenceof its potential carcinogenic impact remains unsubstantiated.

In the current M194 pyrotechnic formulation, the dense yellow smoke isformed by the cost effective reduction-oxidation (redox) reaction ofrelatively inexpensive potassium chlorate (an oxidizer), with sugar (afuel, or reducing agent)—which generates significant heat. The heat, inturn, causes the dye molecules, i.e. the VAT Yellow 4 andbenzanthrone—to enter the gas phase (via sublimation) and begin todisperse. After dispersion of the dye molecules, contact with the coolambient air causes them to condense back to the solid phase, helped bythe presence of sodium bicarbonate, which functions as an evaporativecooling agent. Lastly, the formulation contains a binder to “glue” ittogether, i.e. vinyl alcohol acetate resin (VAAR).

As the binder in the current yellow smoke M194 formulation is availableonly in a solvent media—the manufacturing process requires that thissolvent be driven-off prior to the consolidation of the yellow smokeformulation and its packing into a steel canister within the M194 HHS.

An alternative yellow pyrotechnic smoke formulation has been developedfor the simulation of the smoke signature related to ground-launchedmissiles—part of a Battle Effects Simulator (BES) system. These yellowsmoke formulations use an alternative yellow smoke agent, quinolineyellow spirit solution, also commonly known as quinoline yellow ss orsolvent yellow 33, in combination with potassium chlorate (theoxidizer), sugar (the fuel/reducing agent), magnesium carbonate (acoolant), stearic acid (a lubricant), and VAAR (a binder). However,while these alternative BES yellow smoke formulations are much safer andmore environmentally friendly than the M194 yellow smokeformulations—the burn times are far outside that required for the M194HHS application, i.e about 37.5 seconds (over twice the maximum timeallowed for the M194 yellow smoke application of 9 to 18 seconds).

Therefore, there is a need in the art for a replacement M194 HHS yellowsmoke composition that continues to utilize the relatively inexpensivepotassium chlorate and sugar redox reaction, and contains an alternativeyellow smoke agent that is non-toxic and environmentally safe; whichcomposition will burn for the requisite 9 to 18 seconds, while producingthe desired dense, highly visible yellow smoke. Further, there is also aneed in the art for an all solid ingredient alternative M194 HHS smokecomposition that will rot require any solvent to be driven off duringits manufacture—thereby simplifying and making the manufacturing processmore effective, efficient, and economical.

SUMMARY OF INVENTION

In order to overcome the above stated problems of the prior art—thepresent inventive HHS yellow pyrotechnic smoke formulation preferablycontains all solid, powder ingredients which are easily combined via aconventional dry-tumble process—the ingredients being: potassiumchlorate (KClO₃), an oxidizing agent; sugar (sucrose), a fuel (reducingagent); solvent yellow 33 (SY33, otherwise known as quinoline yellow ss,or as D&C Yellow No. 11), the yellow smoke agent; hydromagnesite(Mg5(CO3)4(OH)2.4H2O), a coolant; stearic acid, a lubricant; hydrophobicfumed silica (available from the Cabot Corporation, under the trademarkCab-O-Sil®), an anti-caking agent; and polyvinyl alcohol (PVA), abinder. These ingredients provide an inventive yellow smoke formulationwherein a redox reaction of the potassium chlorate and sugar formspotassium chloride, carbon dioxide, water vapor, and soot/carbon—whichreaction is exothermic. This exothermic reaction releases sufficientheat to cause the yellow smoke agent SY33 to sublimate, disperse over awide area, and then condense into the desired dense, highly visibleyellow smoke. Further, and most importantly, the burn time is within the9 to 18 second desired, required, smoke production time, when theinventive formulation is compressed into a smoke pellet usable in anM194 HHS.

In an alternative embodiment of the present invention, a small quantityof fumed silica (also known as pyrogenic silica or Cab-O-Sil®),) can besubstituted for an equal quantity of the fuel, sugar—the silica actingas an anticaking agent—to aid in the flowability of the inventiveformulation during its handling, transport, and packing into the desiredHHS container.

If desired, the inventive formulation can contain the alternativebinders polyvinyl alcohol (PVA) and/or nitrocellulose (NC). The NCalternative embodiment, wherein the nitrocellulose ingredient iscontained within solvent media, will require that after the ingredientsare added to the mixture, the resulting now wet mixture will have to bedried in a dryer or oven. When the preferred alternative binderpolyvinyl alcohol is utilized in the inventive mixture, the resultingdry mix is useful for the subject application as is, i.e. no drying stepis required.

Additional features and advantages of the present invention will be setforth in, or are apparent from, the detailed description of preferredembodiments thereof which follows.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional diagram of the current U.S. Army M194 HHS;regarding which HHS, the inventive yellow smoke “candle” may besubstituted with that of the present invention.

FIG. 2 is the structural chemical formulation of solvent yellow 33,SY33, the preferred non-toxic yellow dye material useful in the presentinvention.

FIG. 3 is a cross-sectional view of a yellow smoke formulation testprototype using the present inventive formulation therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventive HHS yellow pyrotechnic smoke composition ispreferably a mixture of solid materials, including about 34.5 weightpercent of potassium chlorate (KClO₃), an oxidizing agent; about 21.5 toabout 22.0 weight percent of a sugar (sucrose), a fuel (reducing agent);about 36 to about 37 weight percent of solvent yellow 33 (SY33, alsoknown as quinoline yellow ss, or as D&C Yellow No. 11), the yellow smokeagent; about 5.5 weight percent hydromagnesite (Mg₅(CO₃)₄(OH)₂.4H₂O), acooling agent; about 0 to about 1.0 weight percent stearic acid, alubricant; and about 0 to about 0.5 weight percent hydrophobic fumedsilica, an anti-caking agent. To this mixture of solid powderedmaterials, a binder or combination of binders may be added, where themost preferred binder is about 0 to about 1.0 weight percent polyvinylalcohol (PVA), also a solid (such that the resulting mixture need onlybe dry-tumbled to be completed).

As stated above, in an alternative embodiment of the present invention,a smal quantity, about 0.5 wt. %, of fumed silica (also known aspyrogenic silica) can be substituted for an equal quantity of the fuel,sugar—the silica acting as an anticaking agent—to aid in the flowabilityof the inventive formulation during its handling, transport, and packinginto the desired HHS container.

An alternative binder useful in the present invention includesnitrocellulose (NC)—but, this alternative binder is standardly availablein a liquid form, i.e. in a solvent media—such that about 10% by weightmust be added and then the solvent driven-off in an oven ordryer—whereby the final quantity of the nitrocellulose is at the desiredabout 0 to about 1.0 weight percent of the total inventive yellow smokeformulation.

The particular yellow smoke agent useful in the present invention is, asstated above, solvent yellow 33—which material is abbreviated as SY33,and also known as quinoline yellow ss, or as D&C Yellow No. 11. As shownin FIG. 2, the chemical structure of SY33 consists of a quinoline carbonskeleton and may be described as 2-(2-quinolyl)-1,3-indandione. Thismaterial is conventionally used as a coloring agent in topical drugs andcosmetics, in spirit lacquers, acrylic resins, polystyrene,polycarbonates, polyamides and to color hydrocarbon solvents. Mostimportantly, SY33 has been deerred admissible by the U.S. Army PublicHealth Command (PHC) in colored smoke formulations and this dye ispresently used in M18 smoke grenade production. Also, inhalation studiesof SY33 as a smoke dye indicates that this compound is cleared from thelungs very rapidly.

The specification of the various ingredients in the above detailedinventive formulation preferably meet the criteria and specificationsshown in Table 1 below.

TABLE 1 Preferred chemical specifications for the ingredients useful inthe present invention. Ingredient Specification (US MilitarySpecifications) Potassium chlorate (KClO₃) MIL-P-150D, Grade B, Class 7Sugar (sucrose) MIL-AA-20135D, Type 1, Style C Solvent yellow 33MIL-DTL-51485B(EA), Type II, from Nation Ford Chemical Sodiumbicarbonate Technical grade, from Hummel Croton (NaHCO₃) HydromagnesiteTechnical grade, from Pine Bluff Arsenal (Mg₅(CO₃)₄(OH)₂•4H₂O) Stearicacid MIL-S-271B Hydrophobic fumed silica From Cabot (Cabosil) VAARMIL-V-50433 Polyvinyl alcohol Molecular weight range: 77,000-79,000g/mol Nitrocellulose Technical grade, from Alliant Techsystems

In preparing the inventive yellow smoke formulation, the potassiumchlorate was initially oven dried overnight at 140 degrees F.—to ensureits dryness. Then, in the case of the inventive formulation embodimentscontaining only solid ingredients, the potassium chlorate and otheringredients were tumbled end-over-end in conductive plastic containersfor 60 min; while, those containing wet NC were blended in a Hobartmixer for 30 min. Dry-tumbled formulations were taken directly toloading operations without further processing, while NC-basedformulations were oven-cured overnight at 140° F. prior to loading.Following blending, the dry mixture was hydraulically pressed into kraftcardboard tubes—which is a distinct advantage over formulations of theprior art. Specifically, the current inventive yellow smoke formulationcan be consolidated and delivered in the prior art steel canister, or inother canister materials, such as an aluminum, or even cardboardcanisters—and still give the requisite smoke density, color, andduration of burn. And, after consolidation and coating with first-firecomposition, the pressed pellets are ready for evaluation/testing.

The inventive formulations were tested and proved to meet the requisitesmoke density, color, and burn time in biodegradable cardboard tubes (asshown in FIG. 3)—using static ignition tests. Referring to FIG. 3, a70-gram, cylindrical smoke pellet was pressed in 2-3 increments (atabout 4,000 to about 12,000 pound dead load, for about 4 seconds dwelltime) inside of a Kraft paper tube—to form a smoke candle. A thin coatof igniter slurry (first-fire composition) was applied to the topsurface (shallow recess on the left side of the pressed smokecomposition) and tapered inner bore of the pellet. After oven-curing at140° F. for 16 hours, the pellet (smoke candle) was ready to beignition-tested and its resulting smoke density, color, and burn timeevaluated.

The inventive formulations were tested against the current BES yellowsmoke formulation, which was considered a baseline, as it is similar inmany respects; but, as stated, has a burn time that is totallyunacceptable (twice the maximum allowed rate of 18 seconds). The resultsof the tests are shown in Table 2, and the summarized below:

-   -   (1) replacement of the binder present in BES—samples designated        12 and 14, or eliminating the binder altogether, designated        13—resulted in burn times on the outer cusp of the requirement        ˜18 s in each case—and were judged not acceptable;    -   (2) increasing oxidizer content in 5 wt. % increments,        designated 15 and 16, yielded burn times more-or-less equivalent        to that of the BES control—i.e. not acceptable;    -   (3) increasing dye content in 5 wt. % increments, designated 17        and 18 yielded burn times that were both longer than the BES        control—i.e. not acceptable;    -   (4) substituting the coolant NaHCO₃ for hydromagnesite        (Mg₅(CO₃)₄(OH)₂.4H₂O) the in the BES control, was met with a        significant improvement in burn time, demonstrated by burning of        the formulation designated 19—however, not to the extent as to        be acceptable. This coolant effect was also explored in the        alternative formulations, designated 22, 24, and 25, which were        identical to formulations designated 12, 13, and 14, again only        using NaHCO₃ instead of (Mg₅(CO₃)₄(OH)₂.4H₂O) as a coolant.        These too, unfortunately, burned outside the acceptable/target        time range;    -   (5) a mix identical to 12 only with 2 wt. % NC, designated 23,        gave a burn time that was still too long; despite efforts to        reduce burn time and the improvements exhibited by 12, 13, and        14, more formulation development was necessary to fit more        comfortably within the target time range (ideally 13-15        seconds);    -   (6) tests at 10.5 wt. % coolant weight percentage for all four        binder systems (NC, PVA, binder-free, and VAAR) designated 89        through 117, and 118 through 121 proved unacceptably long, with        the (Mg₅(CO₃)₄(OH)₂.4H₂O)-based formulations generally burning        faster than the NaHCO₃-based formulations;    -   (7) however, surprisingly, three formulations in the grouping        designated 27, 28, and 29, at 5.5 wt. % (Mg₅(CO₃)₄(OH)₂.4H₂O)        met the target burn time range, each at about 15 seconds; but    -   (8) the alternative NaHCO₃-based formulations, designated 26        through 64 at this 5.5 wt. % coolant level—still burned outside        the target range;    -   (9) further, and also surprisingly, as the coolant level was        progressively lowered, while we expected to see even shorter        burn times by cutting the coolant level to 2.5 wt. % in the        grouping designated 77 through 80, and 81 through 84—these        formulations, however, generally gave smoke plumes of        drastically reduced color quality. Apparently, the coolant level        in this last grouping was not sufficiently high to moderate the        reaction temperature and to suppress flaming.

TABLE 2 Chemical composition and performance of invented yellow smokeformulations^(a), 27, 28, 29, and similar compositions which failed tomeet the burn time standard Wt. % Burn Ref. Wt. % Wt. % Wt. % Wt. % Wt %fumed Time No. KClO₃ Sugar Coolant^(c) NaHCO₃ SY 33 Binder silica (sec)BES 29.5 22 15.5 31 VAAR 38 12 29.5 22 15.5 31 NC 19 13 29.5 22 15.5 32None 17 14 29.5 22 15.5 31 PVA 18 15 29.5 27 10.5 31 VAAR 42 16 29.5 325.5 31 VAAR 34 17 29.5 22 10.5 36 VAAR 43 18 29.5 22 5.5 41 VAAR 45 1929.5 22 15.5 31 VAAR 22 22 29.5 22 15.5 31 NC 30 24 29.5 21.5 15.5 31PVA 0.5 42 25 29.5 21.5 15.5 32 None 0.5 36 23 29.5 22 14.5 31 NC (2%)25 89 29.5 22 10.5 36 NC 23 90 29.5 21.5 10.5 37 None 0.5 34 116 29.521.5 10.5 36 PVA 0.5 33 117 29.5 22 10.5 36 VAAR 86 118 29.5 22 10.5 36NC 49 119 29.5 21.5 10.5 37 None 0.5 42 120 29.5 21.5 10.5 36 PVA 0.5 33121 29.5 22 10.5 36 VAAR 65 27 34.5 22 5.5 36 NC 16 28 34.5 21.5 5.5 37None 0.5^(b) 15 29 34.5 21.5 5.5 36 PVA 0.5^(b) 15 63 34.5 22 5.5 36VAAR 49 26 34.5 22 5.5 36 NC 24 33 34.5 21.5 5.5 37 None 0.5 21 34 34.521.5 5.5 36 PVA 0.5 20 64 34.5 22 5.5 36 VAAR 88 77 34.5 22 2.5 39 NC 2178 34.5 21.5 2.5 40 None 0.5 24 79 34.5 21.5 2.5 39 PVA 0.5 17 80 34.522 2.5 39 VAAR 55 81 34.5 22 2.5 39 NC 28 82 34.5 21.5 2.5 40 None 0.526 83 34.5 21.5 2.5 39 PVA 0.5 26 84 34.5 22 2.5 39 VAAR 54 ^(a)Allformulations contain 1 wt. % stearic acid as a lubricant and, exceptthose noted otherwise or those binder-free, 1 wt. % binder (NC or PVA orVAAR - as stated). ^(b)The fumed silica, e.g. Cab-O-Sil ® available fromthe Cabot Corporation, can be omitted entirely and the sugar contentincreased correspondingly to 22 wt. % with no difference in performance.^(c)The coolant being: hydromagnesite (Mg₅(CO₃)₄(OH)₂•4H₂O).

The procedure used in the static ignition tests, whose results aredetailed above, involved using the cylindrical smoke pellets, or smokecandles, (produced as detailed above), wherein the pellet were clampedvertically with the top slurry-coated end facing up. The head of anelectric match was placed on the top slurried end. After passing anenergy of 2 volts through the electric match, the resulting spit of theelectric match lights the igniter slurry. The heat from this ignitionevent then initiates a reduction-oxidation reaction between the fuel(sugar) and the oxidizer (potassium chlorate) in the tested pressedsmoke compositions. The burning of the pressed pellet propagated in acore-burning fashion, from top-down and from inside-out (butsurprisingly, not bottom-up). The burn times, linear burning rates, andmass consumption rates were measured for all smoke candles tested—andthe results presented above.

Although the invention has been described above in relation to preferredembodiments thereof, it will be understood by those skilled in the artthat variations and modifications can be effected in these preferredembodiments without departing from the scope and spirit of theinvention.

1. A HHS yellow smoke composition having a burn time of about 15seconds, comprising:
 1. a mixture of about 34.5 weight percent of anoxidizer, wherein the oxidizer is potassium chlorate;
 2. about 21.5 toabout 22.0 weight percent of a fuel, wherein the fuel is sucrose; 3.about 36 to about 37 weight percent of quinoline yellow ss;
 4. about 5.5weight percent of a coolant, wherein the coolant is hydromagnesite; 5.about 0 to about 1.0 weight percent of a lubricant, wherein thelubricant is stearic acid;
 6. about 0 to about 1.0 weight percent of abinder, wherein the binder is polyvinyl alcohol;
 7. wherein, when themixture is compressed into a smoke pellet.
 2. The HHS yellow smokecomposition of claim 1, wherein
 1. the oxidizer is potassium chlorate;2. the fuel is sucrose;
 3. the coolant is hydromagnesite;
 4. thelubricant is stearic acid; and
 5. the binder is polyvinyl alcohol. 3.The HHS yellow smoke composition of claim 2, wherein the binder isnitrocellulose.
 4. The HHS yellow smoke composition of claim 1, whereinthe mixture is compressed at from about 4,000 to about 12,000 pound deadload, for a period of about 4 seconds, to form the smoke pellet.
 5. TheHHS yellow smoke composition of claim 1, wherein about 0 to about 0.5weight percent of an anticaking agent is included in the mixture and anequal quantity of the fuel is removed.
 6. The HHS yellow smokecomposition of claim 6, wherein the anticaking agent is hydrophobicfumed silica.
 7. The HHS yellow smoke composition of claim 4, whereinthe composition is compressed inside of a biodegradable cardboard tube.